Python测试是否存在对象 [英] Python test if object exists

问题描述

我认为使用try的不好的风格：除了：对于流控制，但是我无法弄清楚如何编写以下代码来测试Django中的DB字段是否存在。这是肮脏的代码：

I consider it bad style to use try: except: for flow control, but I can't figure out how to write the following code to test if a DB field in Django exists. This is the "dirty" code which works:

@receiver(pre_save, sender=UserProfile)
def create_user_profile(sender, instance=None, **kwargs):

    try:
        print str(instance.bank_account)
    except:
        print 'No account'

我宁愿做这样的事情，但是当 if 语句运行，对象不存在：

I would rather wanna do something like this, but I get an exception when the if statement is run and the object does not exist:

@receiver(pre_save, sender=UserProfile)
def create_user_profile(sender, instance=None, **kwargs):

    if instance.bank_account is None:
        print 'No account'
    else:
        print str(instance.bank_account)

推荐答案

猜测你遇到一个 BankAccount.DoesNotExist 错误？如果是这样，您可以扭转 UserProfile 和 BankAccount 之间的关系。看看 Django ticket＃10227 了解这里发生了什么。

I'm guessing you encounter a BankAccount.DoesNotExist error? If that's the case, you could reverse the relationship between UserProfile and BankAccount. Have a look at Django ticket #10227 to find out what's going on here.

就是说，如果我需要使用你的代码，我宁愿看到一个明确的尝试...除了而不是一个解决方法，除非该解决方法实际上是有意义的。

That being said, if I needed to work with your code I'd rather see an explicit try...except instead of a workaround, unless that workaround actually makes sense.

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